1. Field of Invention
The present invention relates in general to circuit assemblies, such as printed circuit boards (PCBs), and other objects that are sensitive to electrostatic discharge (ESD). More particularly, the present invention relates to protecting objects that are sensitive to ESD by using nested plates to direct the flow of ESD current to a targeted impedance.
2. Background Art
Electrostatic discharge (ESD) is the sudden and momentary electrical current that flows between two objects at different electrical potentials. These momentary electrical currents may disturb or cause damage to circuit assemblies, such as printed circuit boards (PCBs), and other objects that are sensitive to ESD.
Circuit assemblies are typically populated with integrated circuits (ICs) that are made from materials (i.e., electrically conductive materials, semiconductor materials and insulator materials) susceptible to disruption or permanent damage when subjected to the voltages associated with an ESD event. For example, electrostatic charges that accumulate on an enclosure of an electronic device can create a high voltage that may discharge into the ICs of circuit assemblies within the enclosure. The voltage applied to the ICs through this ESD event can alter the state of and/or cause damage to one or more of the ICs.
Typically, ESD events are caused by static electricity. Static electricity can build up on objects and people. For example, static electricity can be generated through tribocharging. Tribocharging is the separation of electric charges that occurs when two dissimilar materials interact, e.g., the materials are brought into contact and separated. Perhaps the best known example of tribocharging occurs when a person walks on a rug. The resulting build up of electrostatic charge on that person can lead to an ESD event (e.g., a spark) when the person comes into contact with another person or an object such as an electronic device.
ESD events are also caused by electrostatic induction. Electrostatic induction occurs when an electrically charged object is placed near a conductive object isolated from ground.
Electromagnetic compatibility (EMC) issues can also play a role in ESD events. For example, the emission of electromagnetic waves can cause the build up of electrostatic charge on objects and people.
The most spectacular form of ESD is a spark (sometimes referred to as an “arc”), which occurs when an ionized conductive channel is created in an insulator such as air between two objects at different electrical potentials. A high voltage differential between the two objects may cause the air in the vicinity to ionize and thus create a low impedance path to discharge the high voltage. The result is a spark, which can cause minor discomfort to people, disruption or damage to electronic equipment, and fires and explosions if the air contains combustible gases or particles. For example, methane and coal dust explosions have been caused by electrostatic discharges.
Therefore, a need exists for an enhanced mechanism for protecting objects that are sensitive to ESD.